This invention relates to resins which polymerise on exposure to actinic radiation, to methods of preparing them and of polymerising such resins in water-borne form by means of actinic radiation, to supports bearing thereon such a resin in the polymerisable state, and to substrates bearing thereon a resin polymerised by means of actinic radiation.
Substances capable of becoming polymerised on exposure to actinic radiation are used as surface coatings, e.g., on metals, paper, and card (i.e., boxboard, about 0.1 to 0.5 mm thick, used in the construction of folding cartons). The advantage of using actinic radiation is that the consumption of energy is generally less than when the substances have to be polymerised by the action of heat. Substances commonly employed are the adduct of acrylic acid or methacrylic acid with the diglycidyl ether of bisphenol A, i.e., 2,2-bis(4-(3-acryloyloxy-2-hydroxypropoxy)phenyl)propane or its methacryloyl homologue. However, the viscosity of compositions containing these adducts is generally too high for ease of application, and so low molecular weight photopolymerisable acrylates, such as propylene glycol diacrylate and glycerol triacrylate, are incorporated.
However, the use of volatile, low molecular weight acrylate esters in such compositions is often undesirable, on grounds of toxicity, and so the need exists for resins which may be polymerised by means of actinic radiation and which may be used as surface coatings but do not contain acrylate esters of low molecular weight.
It has now been found that, by using certain novel advanced resins, the aforesaid requirement can be at least substantially met.
In our British Patent Specification No. 1 521 933 we have described resins which are soluble in water before exposure to actinic radiation but which, on exposure to actinic radiation, polymerise and become insoluble in water, the said resins having the formula ##STR2## where
a is an integer of average value of at least 1, but preferably not more than 100,
each R and R.sup.1 represents a group of formula ##STR3## or --O--(OC).sub.c --R.sup.5 --(CO).sub.c --O--,
each R.sup.2 represents a hydrogen atom or a group of formula --(CH.sub.2 NH).sub.d COC(R.sup.6).dbd.CH.sub.2, with the proviso that at least 1, and preferably at least 25%, of the 2a groups R.sup.2 are other than a hydrogen atom,
each R.sup.3 denotes an alkyl group of 1 to 4 carbon atoms, or conjointly each pair represents a group of formula --CH.sub.2 CH.sub.2 --, --C(R.sup.7 R.sup.8)CO--, ##STR4## --CH.sub.2 CH.sub.2 CH.sub.2 --, --COCO--, --COCOCO--, or --COC(OH).sub.2 CO--,
R.sup.4 represents a divalent aliphatic, cycloaliphatic, or araliphatic radical of 1 to 8 carbon atoms, especially an alkylene group of 1 to 6 carbon atoms,
b, c, and d are each zero or 1,
R.sup.5 represents a straight or branched chain aliphatic group of 2 to 20 atoms, such as one of 2 to 9 carbon atoms, especially an alkylene group which may be interrupted by one or more carbonyloxy groups or by one or more ether oxygen atoms, or, providing each c is 1, it may alternatively represent a group of formula ##STR5##
R.sup.6 represents a hydrogen atom or an alkyl group of 1 to 4 carbon atoms, and
R.sup.7 and R.sup.8 each represent a hydrogen atom or a methyl or ethyl group.
The resins of formula I were prepared in two stages. The first involved reaction of a diepoxide of formula IV ##STR6## with a diol, dicarboxylic acid, or heterocycle of formula V EQU H--R.sup.1 --H V
to form an advanced, linear diepoxide of formula VI ##STR7##
In the second stage, some or all of the indicated secondary hydroxyl groups were replaced by groups of formula --O--(CH.sub.2 NH).sub.d COC(R.sup.6).dbd.CH.sub.2 through reaction with e.g., N-(hydroxymethyl)acrylamide or acryloyl chloride.
In British Patent Specification No. 1 367 207 we have described polyacrylates of N-heterocyclic compounds. One of the Examples describes a process in which 1-glycidyl-3-(2-glycidyloxy-n-propyl)-5,5-dimethylhydantoin (0.9 equiv.) is heated with sebacic acid (0.6 equiv.) to form a product having principally the structure ##STR8## where each R.sup.9 denotes a glycidyl group.
This diepoxide is then heated with acrylic acid (0.3 equiv.) to form a resin, highly viscous in the cold, to which is ascribed the principal structure VII where each R.sup.9 now denotes a 3-acryloyloxy-2-hydroxypropyl group.
In British Patent No. 1 399 135 we have described the polymerisation of such polyacrylates as that of formula VII where each R.sup.9 denotes a 3-acryloyloxy-2-hydroxypropyl group by means of ionising radiation.
We have now found that novel acryloyl or methacryloyl-containing resins may be prepared and substantially meet the aforesaid requirements. While not necessarily fully soluble in water they are miscible with it, and can be applied containing limited amounts (e.g., from 5 to 25% by weight) of water for ease of application.